Discrepancies between genetic and ecological divergence patterns suggest a complex biogeographic history in a Neotropical genus

Abstract

Phylogenetic patterns and the underlying speciation processes can be deduced from morphological, functional, and ecological patterns of species similarity and divergence. In some cases, though, species retain multiple similarities and remain almost indistinguishable; in other cases, evolutionary convergence can make such patterns misleading; very often in such cases, the “true” picture only emerges from carefully built molecular phylogenies, which may come with major surprises. In addition, closely related species may experience gene flow after divergence, thus potentially blurring species delimitation. By means of advanced inferential methods, we studied molecular divergence between species of the Virola genus (Myristicaceae): widespread Virola michelii and recently described, endemic V. kwatae, using widespread V. surinamensis as a more distantly related outgroup with different ecology and morphology—although with overlapping range. Contrary to expectations, we found that the latter, and not V. michelii, was sister to V. kwatae. Therefore, V. kwatae probably diverged from V. surinamensis through a recent morphological and ecological shift, which brought it close to distantly related V. michelii. Through the modeling of the divergence process, we inferred that gene flow between V. surinamensis and V. kwatae stopped soon after their divergence and resumed later, in a classical secondary contact event which did not erase their ecological and morphological differences. While we cannot exclude that initial divergence occurred in allopatry, current species distribution and the absence of geographical barriers make complete isolation during speciation unlikely. We tentatively conclude that (a) it is possible that divergence occurred in allopatry/parapatry and (b) secondary contact did not suppress divergence.

Disentangling the causes of high polymorphism sharing in sympatric Petunia species from subtropical highland grasslands: insights from nuclear diversity

“…The divergence from a common ancestor expanding its range is primarily based on stochastic processes such as drift, mutation, and recombination. Ancestral gene flow detected between Petunia species from the SHG is consistent with phylogenetic radiation without strict reproductive isolation, a property of the mechanisms of maintenance of genetic integrity in species complexes as observed in other Neotropical species (e.g., Binelli et al, 2020). Four endemic Calibrachoa species also occur in SHG.…”

“…The climate shifts and vegetation contraction-expansion dynamic are often pointed out as the primary driver of species richness and endemism observed in SHGs ( Iganci et al, 2011 ). In turn, isolation can interrupt the gene flow and, if it occurs rapidly and intensely, promotes speciation with low differentiation ( Binelli et al, 2020 ), intensifying the speciation rates (e.g., Lorenz-Lemke et al , 2010 ; Mäder and Freitas, 2019 ).…”